The invention relates to a process for the production of a titanium alloy part with good characteristics, intended for use e.g. as compressor disks for aircraft propulsion systems, as well as to the parts obtained.
FR No. 2 144 205 (GB No. 1356734) describes a titanium alloy with the following composition by weight: Al 3 to 7, Sn 1 to 3, Zr 1 to 4, Mo 2 to 6, Cr 2 to 6 and up to approximately 0.2% O, 6% V, 0.5% Bi, the remainder being Ti and impurities. The preferred values are Al 4.5 to 5.5, Sn 1.5 to 2.5, Zr 1.5 to 2.5, Mo 3.5 to 4.5, Cr 3.5 to 4.5 and up to approximately 0.12% O. The corresponding forged parts or forgings undergo a double heat treatment of the solid solution firstly between 730.degree. and 870.degree. C. and then between 675.degree. and 815.degree. C., followed by thermal ageing or annealing at between 595.degree. and 650.degree. C. Sample 4 (Al 5-Sn2-Zr2-Mo4-Cr4-O0.08) has the following mechanical characteristics: breaking load 1204 MPa, elastic limit at 0.2% 1141 MPa, crack propagation resistance 88.times.34.8/.sqroot.1000=96.9 MPa. .sqroot.m, creep at 425.degree. C. under 525 MPa=0.2% elongation in 7.2 h and 0.5% elongation in 55 h. The breaking elongation is not given. In practice it has been found that the parts obtained on the basis of this composition and process often had significant segregations leading to ductility and crack propagation resistance (tenacity) losses, whilst also having an inadequate creep resistance. It was found that the aforementioned segregations corresponded to areas enriched in Cr, then causing an embrittlement and that a reduction of the Cr content led to inadequate mechanical properties.
The Applicant attempted to obtain parts of the same type of alloy with a regular structure, no segregations and high mechanical characteristics at 20.degree. C. (Rm-R.sub.p0.2 -K.sub.1C) with an adequate elongation, as well as a significantly improved creep behaviour at 400.degree. C.